巴基斯坦N区块浪控三角洲沉积相划分及模式

Sedimentary Facies Division and Model of Wave-Controlled Delta of N Block, Pakistan

浪控三角洲砂体是海陆交互带沉积有利的油气储层和勘探目标,目前业界对其微相划分、沉积机理和沉积模式研究较少。以巴基斯坦N区块为例,依据岩心、测井、地震及分析测试资料,开展受波浪改造作用的海相三角洲沉积相带划分、展布及沉积模式研究。结果表明:综合大量沉积相标志分析,研究区白垩系处于砂质高能海岸带,三角洲入海口受到强烈的波浪、沿岸流和风暴浪的改造、破坏和再分配作用,形成浪控三角洲沉积,表现为沿平原亚相向海洋延伸的环岸砂坝发育带。其格架相与建设性三角洲明显不同,水下分流河道和河口砂坝不发育,在河口两侧形成滩砂复合沉积,具有砂岩质纯、厚层、平行海岸线、大面积连片分布、延伸规模广的特点,构成了浪控三角洲骨干砂体类型。外前缘相带始终受波浪冲洗和扰动,形成了平坦、席状的砂泥互层。平面上为向广海方向凸出的朵叶状轮廓,垂向上为下细上粗的反旋回,微相类型保存不完整,为破坏性三角洲沉积。最后总结了实例区浪控三角洲沉积模式,为三角洲储层评价提供基础。

Wave-controlled deltas are important reservoir types and are potential exploration targets in marine and land interaction deposition. At present,few studies have been reported in the industry regarding microfacies division,sedimentary mechanisms or modeling. Taking N Block in Pakistan as an example,sedimentary facies division and models of marine delta affected by wave flow were studied based on core logging,seismic and test data. In the Cretaceous,N Block had a high-energy coastal zone in which the delta estuary was damaged,transformed and redistributed by strong wave action,coastal currents and storm waves,forming the sedimentary wave-controlled delta. It is represented by a circum-shoreline bar extending from the delta plain to the ocean. Its framework is clearly different from usual delta facies. Underwater distributary channels and mouth bar microfacies have not been developed in the proximal delta front,and a composite sandy beach was formed on both sides of the estuary,with thick layers of pure sandstone parallel to the coastline distributed contiguously over large areas and with wide-extension scale sedimentary characteristics,which is the skeletal sandbody. The distal delta front is always washed and disturbed by waves,forming flat interbedded sheets of sand and mud. In plan,it presents a large area with a lobe shape towards the sea. Vertically,a reverse cycle of upward coarsening was formed. The sedimentary sequence is incomplete,and shows destructive characteristics. Finally,the sedimentary model of a wave-controlled delta in an sample area is summarized,providing a basis for detailed evaluation of sedimentary delta reservoirs.